Traditional state of the art engine oil lubricants often use dialkyldithiophosphate (ZDP) antiwear additives to protect the components of engine in which the oil lubricants are used from high levels of wear. In addition oil lubricants also generally contain ashless dispersants to handle soot and sludge.
A relatively new class of dispersants, those comprising a quaternary ammonium salt, are becoming increasingly important due to their outstanding soot handling and sludge control properties. Such materials are known in the art and are described in references such as U.S. Pat. Nos. 7,951,211 and 7,906,470, and US patent applications 2008/0113890, 2012/0138004, to name a few.
However, in some instances the use these quaternary ammonium salts in combination with dialkyldithiophosphate antiwear additives, especially in high temperature applications, may lead to mixtures that do not have good seal and/or elastomer compatibility, especially with fluoro elastomers. It is believed that these materials may interact with one another to result in materials that may degrade or even destroy fluoroelastomers, including seals made from such fluoroelastomers. Fluoroelastomers are fluorocarbon-based synthetic rubbers and are considered to generally have good chemical resistance and physical properties, including under high temperature conditions. Thus such materials are widely used to make seals. Examples of specific fluoroelastomers include copolymers and/or terpolymers of hexafluoropropylene, vinylidene fluoride, tetrafluoroethylene, and perfluoromethylvinylether. Such materials include those marketed under the Viton® trade name by DuPont™. This issue with using quaternary ammonium salt dispersant in combination with dialkyldithiophosphate antiwear additives may limit how broadly this new class of quaternary ammonium salt dispersants may be used or force oil lubricant users to remove dialkyldithiophosphate antiwear additives, leading to wear problems.
There is need for a lubricating composition that uses quaternary ammonium salt dispersants in combination with dialkyldithiophosphate antiwear additives while providing a balance of deposit control, wear performance, and seal compatibility. The present invention does just that.